Apparatus and method for transmitting/receiving broadcast data in a mobile communication system

ABSTRACT

A method and apparatus for transmitting a broadcast physical layer packet in a mobile communication system supporting multi-slot transmission and hybrid Automatic Repeat Request (H-ARQ) are provided. The method comprises initially transmitting the broadcast physical layer packet according to a fixed transmission format for at least one first slot interval and retransmitting the broadcast physical layer packet for at least one second slot interval using a variable transmission format different from the transmission format used in the first slot interval.

PRIORITY

This application claims the benefit under 35 U.S.C. §119(a) ofapplication Serial No. 2005-52675, filed in the Korean IntellectualProperty Office on Jun. 17, 2005, and application Serial No. 2005-85452,filed in the Korean Intellectual Property Office on Sep. 13, 2005, theentire disclosures of both of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an apparatus and method fortransmitting/receiving data in a mobile communication system. Moreparticularly, the present invention relates to an apparatus and methodfor transmitting/receiving broadcast data in a mobile communicationsystem.

2. Description of the Related Art

In general, mobile communication systems have been developed to supportunicast service. The “unicast service” refers to the communicationbetween a base station and one mobile station. That is, in the unicastservice, the base station transmits data only to one mobile station,instead of transmitting the same data to a plurality of mobile stations.The voice service and various data services are the typical unicastservices.

With the rapid progress of wireless communication technology, systemscapable of enabling users to receive broadcast service while on the movehave recently been developed and deployment thereof is at hand. The“broadcast service” refers to a process of transmitting the same servicedata from a base station to a plurality of mobile stations. Thebroadcast service can provide not only general over-the-air broadcastservice but also a plurality of private broadcast services, anddeployment of Digital Multimedia Broadcasting (DMB) service is close athand.

Various attempts are being made to provide broadcast service even inmobile communication systems, and many schemes have been proposed sofar. A High Rate Packet Data (HRPD) system proposed in 3rd GenerationPartnership Project 2 (3GPP2) is a typical example of the system capableof supporting broadcast service among the mobile communication systemsproposed up to now.

The HRPD system adopts a unicast transmission method as its basictransmission method, and also employs hybrid Automatic Repeat Request(H-ARQ). In addition, a Code Division Multiplexing (CDM)-basedtransmission method and an Orthogonal Frequency Division Multiplexing(OFDM)-based transmission method have been proposed as an example of atransmission method for Broadcast/Multicast Service (BCMCS) recentlydiscussed in the mobile communication system. Herein, “BCMCS” refers tothe broadcast service provided in the HRPD system, for convenience. Amethod for transmitting broadcast signals using H-ARQ uses a scheme fordividing one encoder packet (EP) into a plurality of sub-packets andtransmitting the sub-packets using a plurality of slots, like theunicast scheme. A receiver receiving the sub-packets performs decodingthereon by combining the sub-packets using an Incremental Redundancy(IR) scheme. That is, a difference between the Broadcast/Multicast(BCMC) transmission scheme and the unicast transmission scheme lies inthat if a mobile station transmits no response signal (ACK/NACK) to abase station in response to received data, the base station transmits aplurality of sub-packets constituting an encoder packet for apredetermined time corresponding to a predetermined number of slots. Inthe HRPD system, the unicast scheme and the BCMC scheme use the commonencoding and decoding methods, and the well-known turbo encoding schemecan be used as the encoding method.

Most mobile communication systems for transmission packets, includingthe HRPD system, transmit data using multi-slot interlacing schemes. Ofthe multi-slot interlacing schemes, a 4-slot interlacing scheme is mosttypical.

With reference to FIG. 1, a description will now be made of the 4-slotinterlacing scheme.

FIG. 1 is a timing diagram for a description of a 4-slot interlacingscheme used in an HRPD system.

As illustrated in FIG. 1, a transmitter transmits data to a receiver atintervals of 4 slots. That is, the transmitter performs firsttransmission (1st TX) 100 at a time of t0 to t1. The transmitted signalis received at the receiver before a time t2, and then processed.Thereafter, the receiver transmits a response signal (ACK/NACK) 105 inresponse to the first received signal 100. The response signal arrivesat the transmitter before a time t4. If the response signal transmittedby the receiver indicates ACK (Good Reception), the transmittertransmits the next data. However, if the response signal transmitted bythe receiver indicates NACK (Poor Reception), the transmitterretransmits the first transmitted data. For the retransmission, thetransmitter performs second transmission (2nd TX) 110 in response to theresponse signal from the receiver at a time of t5 to t6. Similarly, thetransmitted signal is received at the receiver before a time t7, andthen processed. The receiver transmits a response signal (ACK/NACK) 115in response to the received signal. The response signal arrives at thetransmitter before a time t9.

As described above, based on the response signal from the receiver, thetransmitter determines whether it will perform initial transmission orretransmission on the transmission data. That is, the transmitterperforms the transmission at intervals of 4 slots. Therefore, for theremaining 3 slots where transmission to the receiver is not performed,the transmitter can transmit data to another mobile station, or cantransmit data other than the currently transmitted data to the receiverusing the remaining slots. This scheme is called the 4-slot interlacingscheme.

The 4-slot interlacing scheme is used for the following reasons. Afterthe transmitter transmits a part of or all of the coded symbol createdusing one packet, if the receiver fails to receive the transmitted codedsymbol, the transmitter should retransmit a part of or all of the codedsymbol of the corresponding packet to increase reception capability ofthe receiver. In the HRPD system, the maximum number of retransmissionsis limited to a predetermined value.

The use of the 4-slot interlacing scheme can provide different broadcastservices at intervals of a predetermined number of slots. A descriptionthereof will be made with reference to FIG. 2.

FIG. 2 is a timing diagram for a description of a scenario in whichdifferent broadcast services are provided at intervals of every slot inan HRPD system supporting a 4-slot interlacing scheme.

It is assumed in FIG. 2 that each of the parts hatched with obliquelines indicates a slot corresponding to a multiple of 4 (4 n), and eachof the parts hatched with horizontal lines indicates a slot that comesone slot after the multiple of 4. The slots hatched with the obliquelines and the slots hatched with the horizontal lines are the slotsallocated for a particular broadcast service. It can be noted that the4-slot interlacing scheme is applied even to the slots allocated for thebroadcast service. A description will now be made of an exemplary methodfor transmitting packet data through each of the slots allocated for thebroadcast service.

In FIG. 2, reference numeral 211 represents initial transmission of afirst packet P1, reference numeral 212 represents first retransmissionof the first packet P1, and reference numeral 213 represents secondretransmission of the first packet P1. Thereafter, in the same slot ofthe interlacing scheme, the next packet, in other words a third packetP3 231 is transmitted. Although the number of transmissions is set suchthat one data packet can be transmitted up to 3, the number oftransmissions is subject to change. Similarly, for a second packet P2,initial transmission 221, first retransmission 222 and secondretransmission 223 are performed, and thereafter, the next packet, inother words a fourth packet P4 241 is transmitted. Similarly, for thethird packet P3 and the fourth packet P4, initial transmissions 231 and241, first retransmissions 232 and 242, and second retransmissions 233and 243 are performed.

Various messages provided in the system to provide the broadcast serviceand a method for providing the broadcast service will now be describedin detail hereinbelow. The HRPD system transmits packet transmissioninformation for receipt of a broadcast physical layer packet(hereinafter simply referred to as “packet” ) for BCMCS using anoverhead signaling message, for example a broadcast overhead message.The overhead signaling message includes therein a BCMC flow IDtransmitted in the cell, information on Frequency Allocation (FA) fortransmitting each BCMCS packet, position information of transmissionslots, a data rate, the number of transmission slots, and Reed-Solomon(RS) coding information. A mobile station, after receiving the BCMCSoverhead message, receives a corresponding packet in a correspondingslot using transmission information of the BCMCS packet that the userdesires to receive.

Generally, because the BCMCS transmits the same information to aplurality of mobile stations, every base station transmits the samepackets in a BCMCS slot in order to provide the BCMCS in the mobilecommunication system. The mobile station receives the packets from thebase stations at once, and increases its reception performance throughsoft combining, noticeably increasing the performance compared with themethod of receiving packets using a signal received from one cell.

The BCMCS transmits data over multiple slots by using the sametransmission format in each slot. In this case, the BCMCS increases thenumber of retransmissions in the area where the reception performance islower. The BCMCS uses the same transmission format, in other words thesame OFDM symbol structure or modulation scheme, even in the area wherethe number of transmissions slots increases.

A structure of the OFDM symbol used in the BCMCS is designed taking intoaccount the surrounding environment such as the maximum signal delay inthe area where the receiver is located. Therefore, at the retransmissiontime, only some neighbor cells participate in the retransmission,reducing the maximum signal delay value of the OFDM signal that thereceiver desires to receive. Generally, a Cyclic Prefix (CP) is insertedin the OFDM symbol taking the maximum signal delay into consideration. Asize of the CP depends upon the possible amount of transmission data.That is, an increase in the size of the CP causes a decrease in thepossible amount of transmission data, and a decrease in the size of theCP increases the possible amount of transmission data. However, thecurrent BCMCS scheme does not take the changed surrounding environmentinto account during retransmission, and uses the fixed transmissionformat. As a result, the CP is set unnecessarily long, causing a wasteof radio resources.

Accordingly, there is a need for an improved apparatus and method fortransmitting and receiving broadcast data in a mobile communicationsystem.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention address at least theabove problems and/or disadvantages and provide at least the advantagesdescribed below. It is, therefore, an object of the present invention toprovide an apparatus and method for adaptively transmitting dataaccording to the surrounding environment when providingBroadcast/Multicast Service (BCMCS) using a multi-slot transmissionscheme in a high-speed mobile communication system.

It is another object of the present invention to provide an apparatusand method for providing BCMCS by transmitting data in a variabletransmission format according to the number of retransmissions in ahigh-speed mobile communication system.

It is further another object of the present invention to provide atransmission/reception apparatus and method for increasing efficiency ofradio resources while providing BCMCS in a high-speed mobilecommunication system.

According to one exemplary aspect of the present invention, there isprovided a method for transmitting a broadcast physical layer packet ina mobile communication system supporting multi-slot transmission andhybrid Automatic Repeat Request (H-ARQ). The method comprises initiallytransmitting the broadcast physical layer packet according to a fixedtransmission format for at least one first slot interval andretransmitting the broadcast physical layer packet for at least onesecond slot interval using a variable transmission format different fromthe transmission format used in the first slot interval.

According to another exemplary aspect of the present invention, there isprovided a method for receiving a broadcast physical layer packet in amobile communication system supporting multi-slot transmission andhybrid Automatic Repeat Request (H-ARQ). The method comprises receivingtransmission format information for the broadcast physical layer packetthrough a broadcast overhead message, receiving the broadcast physicallayer packet that is initially transmitted in a fixed transmissionformat for at least one first slot interval, according to thetransmission format information and receiving the broadcast physicallayer packet that is retransmitted in a variable transmission formatdifferent from the transmission format used in the first slot intervalfor at least one second slot interval, according to the transmissionformat information.

According to further another exemplary aspect of the present invention,there is provided an apparatus for transmitting a broadcast physicallayer packet in a mobile communication system supporting multi-slottransmission and hybrid Automatic Repeat Request (H-ARQ). The apparatuscomprises a transmission unit for generating the broadcast physicallayer packet such that initial transmission and retransmission differfrom each other in a transmission format, a radio frequency (RF) unitfor frequency-up-converting the broadcast physical layer packetgenerated in the transmission unit into an RF signal and a controllerfor controlling operations of the transmission unit and the RF unit soas to initially transmit the broadcast physical layer packet accordingto a fixed transmission format for at least one first slot interval, andretransmit the broadcast physical layer packet for at least one secondslot interval using a variable transmission format different from thetransmission format used in the first slot interval.

According to yet another exemplary aspect of the present invention,there is provided an apparatus for receiving a broadcast physical layerpacket in a mobile communication system supporting multi-slottransmission and hybrid Automatic Repeat Request (H-ARQ). The apparatuscomprises a radio frequency (RF) unit for converting the broadcastphysical layer packet received over the air into a baseband signal, areception unit for receiving the broadcast physical layer packetaccording to transmission formats used for initial transmission andretransmission, and restoring the received broadcast physical layerpacket to an original signal and a controller for controlling operationsof the RF unit and the reception unit so as to, upon receipt of abroadcast overhead message including transmission format information forthe broadcast physical layer packet, receive the broadcast physicallayer packet that is initially transmitted in a fixed transmissionformat for at least one first slot interval, according to thetransmission format information, and to receive the broadcast physicallayer packet that is retransmitted in a variable transmission formatdifferent from the transmission format used in the first slot intervalfor at least one second slot interval, according to the transmissionformat information.

According to still another exemplary aspect of the present invention,there is provided a mobile communication system that supports multi-slottransmission and hybrid Automatic Repeat Request (H-ARQ) and provides abroadcast service. The system comprises at least one base station forinitially transmitting a broadcast physical layer packet according to afixed transmission format for at least one first slot interval, andretransmitting the broadcast physical layer packet for at least onesecond slot interval using a variable transmission format different fromthe transmission format used in the first slot interval and at least onemobile station for, upon receipt of a broadcast overhead messageincluding transmission format information for the broadcast physicallayer packet from the base station, receiving the broadcast physicallayer packets that are initially transmitted and retransmitted in thefirst and second slot intervals, according to corresponding transmissionformats.

According to still another exemplary aspect of the present invention,there is provided a transmission method for a mobile communicationsystem that supports multi-slot transmission and hybrid Automatic RepeatRequest (H-ARQ) and uses an Orthogonal Frequency Division Multiplexing(OFDM) transmission scheme. The method comprises allocating at least oneOFDM symbol to a transmission slot as an internal symbol, and allocatingat least one OFDM symbol to each of a left side and a right side of theinternal symbol as a boundary symbol and transmitting the OFDM symbolsuch that the boundary symbol and the internal symbol differ from eachother in a pilot-to-data tone power ratio (PDR) in a first slot intervalwhere initial transmission is performed and a second slot interval whereretransmission is performed.

According to still another exemplary aspect of the present invention,there is provided a method for receiving a broadcast physical layerpacket in a mobile communication system that supports multi-slottransmission and hybrid Automatic Repeat Request (H-ARQ) and uses anOrthogonal Frequency Division Multiplexing (OFDM) transmission scheme.The method comprises receiving transmission format information includingpilot-to-data tone power ratio (PDR) information for at least one firstslot interval where initial transmission for the broadcast physicallayer packet is performed and at least one second slot interval whereretransmission is performed, through a broadcast overhead message andreceiving the broadcast physical layer packet by performing channelestimation for a corresponding slot interval based on the PDRinformation. At least one OFDM symbol is allocated as an internal symboland at least one OFDM symbol is allocated to each of a left side and aright side of the internal symbol as a boundary symbol in each of thefirst and second slot intervals, and the PDR set in the first slotinterval is different from the PDR set in the second slot interval.

According to still another exemplary aspect of the present invention,there is provided a transmission apparatus for a mobile communicationsystem that supports multi-slot transmission and hybrid Automatic RepeatRequest (H-ARQ) and uses an Orthogonal Frequency Division Multiplexing(OFDM) transmission scheme. The apparatus comprises a transmission unitfor allocating at least one OFDM symbol to a transmission slot as aninternal symbol, allocating at least one OFDM symbol to each of a leftside and a right side of the internal symbol as a boundary symbol, andtransmitting the OFDM symbol, the transmission unit including a pilottone inserter for inserting a pilot tone in the OFDM symbol and acontroller for controlling an operation of the pilot tone inserter suchthat the boundary symbol and the internal symbol differ from each otherin a pilot-to-data tone power ratio (PDR) in a first slot interval whereinitial transmission is performed and a second slot interval whereretransmission is performed.

According to still another exemplary aspect of the present invention,there is provided an apparatus for receiving a broadcast physical layerpacket in a mobile communication system that supports multi-slottransmission and hybrid Automatic Repeat Request (H-ARQ) and uses anOrthogonal Frequency Division Multiplexing (OFDM) transmission scheme.The apparatus comprises a reception unit for receiving transmissionformat information including pilot-to-data tone power ratio (PDR)information for at least one first slot interval where initialtransmission for the broadcast physical layer packet is performed and atleast one second slot interval where retransmission is performed,through a broadcast overhead message, and receiving the broadcastphysical layer packet, the reception unit including a channel estimatorfor performing channel estimation for a corresponding slot intervalbased on the PDR information and a controller for, upon receipt of thebroadcast overhead message, controlling an operation of the channelestimator according to the PDR information, and controlling an overalloperation of the reception unit according to the transmission formatinformation. At least one OFDM symbol is allocated as an internal symboland at least one OFDM symbol is allocated to each of a left side and aright side of the internal symbol as a boundary symbol in each of thefirst and second slot intervals, and the PDR set in the first slotinterval is different from the PDR set in the second slot interval.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a timing diagram for a description of a 4-slot interlacingscheme used in an HRPD system;

FIG. 2 is a timing diagram for a description of a scenario in whichdifferent broadcast services are provided at intervals of every slot inan HRPD system supporting a 4-slot interlacing scheme;

FIG. 3 is a diagram illustrating a configuration of a system forproviding a broadcast service according to an exemplary embodiment ofthe present invention;

FIG. 4 is a diagram illustrating an exemplary format of packet dataconstituting one slot for a broadcast service in an HRPD systemaccording to an exemplary embodiment of the present invention;

FIGS. 5A to 5C are diagrams illustrating cell distribution based ontransmission success rate when broadcast service is provided in asynchronous fashion in cell coverage of each base station in a mobilecommunication system according to an exemplary embodiment of the presentinvention;

FIG. 6 is a block diagram illustrating a structure of a base station'stransmitter for transmitting BCMCS traffic according to an exemplaryembodiment of the present invention;

FIG. 7 is a block diagram illustrating an internal structure of areceiver for receiving an OFDM symbol according to an exemplaryembodiment of the present invention;

FIG. 8 is a flowchart illustrating a process of transmitting broadcastservice traffic in a base station according to an exemplary embodimentof the present invention;

FIG. 9 is a flowchart illustrating a process of receiving broadcastservice traffic in a mobile station according to an exemplary embodimentof the present invention; and

FIG. 10 is a timing diagram illustrating a scenario in which tworetransmissions are performed in a 4-slot interlacing scheme accordingto another exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The matters defined in the description such as a detailed constructionand elements are provided to assist in a comprehensive understanding ofthe embodiments of the invention and are merely exemplary. Accordingly,those of ordinary skill in the art will recognize that various changesand modifications of the embodiments described herein can be madewithout departing from the scope and spirit of the invention. Exemplaryembodiments of the present invention will now be described in detailwith reference to the annexed drawings. In the following description, adetailed description of known functions and configurations incorporatedherein has been omitted for clarity and conciseness.

FIG. 3 is a diagram illustrating a configuration of a system forproviding a broadcast service according to an exemplary embodiment ofthe present invention. With reference to FIG. 3, a description will nowbe made of the broadcast service system according to an exemplaryembodiment of the present invention.

In FIG. 3, base stations (base transceiver systems (BTSs)) 311 and 312are the final nodes that provide Broadcast/Multicast Service (BCMCS) toa mobile station (301). The base stations 311 and 312 provide broadcastservices according to the broadcast schemes of their associated systems.It will be assumed herein that the base stations 311 and 312 areassociated with a High Rate Packet Data (HRPD) system. A detailedstructure and operation of the base station for providing the broadcastservice will be described later with reference to the accompanyingdrawings. The base station provides the broadcast service using, forexample, the 4-slot interlacing scheme described in the prior artsection, and transmits data within the maximum number of transmissions.A format of the transmission data will be described in detailhereinbelow. The base stations 311 and 312 are connected to a unicastbase station controller (BSC/PCF) 313 and a multicast base stationcontroller (BSC/PCF) 314, respectively, and operate under the control ofthe corresponding BSCs/PCFs 313 and 314.

The BSCs/PCFs 313 and 314 control operations of the base stations 311and 312, receive BCMC data from upper layers, and transmit the BCMC datato the corresponding base stations 311 and 312. The unicast BSC/PCF 313performs a function of transmitting signaling information, and themulticast BSC/PCF 314 performs a function of transmitting broadcastcontents. In this case, the unicast BSC/PCF 313 may provide the basestations 311 and 312 with the number of transmissions for broadcastservice data, the number of transmission slots, and the positions of thetransmission slots along with a broadcast overhead message. The unicastBSC/PCF 313 is connected to a packet control function (PCF) of an upperlayer or the same layer, and expressed in a single entity.

The PCF in the unicast BSC/PCF 313 takes charge of various controls fora packet data service. The unicast BSC/PCF 313, an upper layer of whichis connected to a packet data service node (PDSN) 315, can interworkwith a BCMC controller 317. The BCMC controller 317 can receive controlinformation for broadcast traffic data or multicast traffic data from acontent provider 319. The multicast BSC/PCS 314 is connected to abroadcast serving node (BSN) 316. The BSN 316 serves to relay anddeliver BCMC contents. The BSN 316 receives broadcast contents from acontent server 318. The content server 318 receives broadcast contentsfrom the content provider 319. In FIG. 3, the bold lines representbearer paths through which broadcast contents are transmitted, and thesolid lines represent signaling paths. The above-mentioned devices arelogical devices, but they may be implemented in a single physical devicein actual implementation.

A detailed description will now be made of operations of the basestation 311 and the mobile station 301 when BCMC is achieved in thesystem described above.

The base station 311 will first be described. The base station 311provides information on a possible broadcast service to the mobilestation 301 through a broadcast overhead message. The broadcast overheadmessage is periodically transmitted, and when the mobile station 301requests transmission of a particular broadcast service, the basestation 311 performs an operation for transmission of the correspondingbroadcast service. That is, if the base station 311 is currentlyreceiving the requested broadcast traffic from the upper layer, ittransmits the broadcast traffic in a multicast fashion. However, if thebase station 311 is not currently receiving the requested broadcasttraffic from the upper layer, it prepares to receive the requestedbroadcast traffic from the upper layer and multicast the receivedbroadcast traffic. Upon completion of the preparation, the base station311 multicasts the requested broadcast traffic so that the mobilestation 301 may receive the broadcast traffic.

Generally, the broadcast signals are transmitted by several basestations at the same time. The base stations 311 and 312 periodicallybroadcast the broadcast overhead messages. All mobile stations locatedin coverage of the base stations 311 and 312 can receive the broadcastoverhead messages, and the mobile station desiring to receive BCMCSshould first receive the periodically transmitted broadcast overheadmessages. Therefore, with the use of the broadcast overhead message, thebase station provides the mobile station with various broadcastreception information, such as a BCMC flow ID, information indicatingwhether it is now providing the broadcast service, a period of thebroadcast slot, an Extended BCMC (EBCMC) transmission format, a pilot todata tone power ratio (PDR), information indicating whether a dual PDRis set, a modulation method and the like.

The base station transmits an EBCMC transmission format of the broadcasttraffic along with the broadcast overhead message according to anexemplary embodiment of the present invention. The EBCMC transmissionformat is a field indicating a particular transmission format. That is,the mobile station 301 and the base station 311 include a transmissionformat therein. Alternatively, the base station 311 provides the EBCMCtransmission format to the mobile station 301 during initialregistration, so the mobile station 301 and the base station 311 can beaware of the transmission format therebetween. Therefore, the basestation 311 transmits the EBCMC transmission format information to themobile station 301 when the mobile station 301 needs it at the initialoperation. The base station 311 and the mobile station 301 according toan exemplary embodiment of the present invention, as they have an EBCMCtransmission format set therein, can determine which format they willuse, simply based on the EBCMC transmission format. In addition, whenthere is a need for authentication of a mobile station, upon receipt ofan authentication request signal from the corresponding mobile station,the base station can forward the authentication request signal to anupper layer to perform the necessary procedure.

The mobile station 301 is an apparatus for receiving unicast or BCMCsignals transmitted by the base station 311. Therefore, as described inthe prior art section, the mobile station 301, when it receives aunicast service, can transmit a response signal (ACK/NACK) to the basestation 311 in response to received data. However, the mobile station301, when it receives BCMCS, receives a broadcast overhead message andbroadcast traffic signal from the base station 311 and processes thereceived broadcast overhead message and broadcast traffic signal. Afterreceiving the broadcast overhead message, the mobile station 301attempts to receive broadcast signals using only the information for itsdesired broadcast service. If there is a need for authentication orregistration, it performs the authentication or registration using aseparate channel. The mobile station 301 can receive a transmissionperiod of corresponding broadcasting, an EBCMC transmission formatindicating a transmission format during multi-slot transmission, a PDR,dual PDR setting information and the like, through the broadcastoverhead message, and receive BCMCS depending on the broadcast overheadmessage.

A description will now be made of a packet structure of the broadcasttraffic transmitted through one slot in the HRPD system.

FIG. 4 is a diagram illustrating an exemplary format of packet dataconstituting one slot for a broadcast service in an HRPD systemaccording to an exemplary embodiment of the present invention.

Referring to FIG. 4, one slot 400 is divided into half slots. The halfslots have the same format, so only the first half slot 410 will bedescribed. The half slot 410 is composed of a total of 1024 chips. Ofthe 1024 chips, the first 400 chips constitute data, the next 64 chipsare used for medium access control (MAC), and the following 96 chipsform a pilot symbol located in the center. Further, the next 64 chipsform MAC, and the last 400 chips form data. It is assumed that the400-chip data is transmitted by CDM if it is unicast data, andtransmitted by OFDM if it is BCMCS data. It is assumed in FIG. 4 thatthe broadcast service type is BCMCS, so the 400-chip data forms one OFDMsymbol.

The one OFDM symbol has a Cyclic Prefix (CP) 411 generated by copyingthe last part of a payload and attaching the copied part to the head ofthe payload. The CP, as described in the prior art section, should havea length corresponding to the maximum transmission delay time in orderto delete inter-symbol interference (ISI). In an exemplary embodiment ofthe present invention, the length of the CP is variable according to thenumber of transmissions. The reason why the length of the CP should bevariable according to the number of transmissions will be described withreference to FIGS. 5A to 5C.

FIGS. 5A to 5C are diagrams illustrating cell distribution based ontransmission success rate when broadcast service is provided in asynchronous fashion in cell coverage of each base station in a mobilecommunication system according to an exemplary embodiment of the presentinvention.

In FIGS. 5A to 5C, each hexagonal cell represents coverage of one basestation, or coverage of one sector. For convenience, it will be assumedherein that one hexagonal cell represents coverage of one base station.In this case, if initial transmission is performed, there is a pluralityof cells 500, 510, 520, 530 and 540 having a poor BCMCS receptioncapability as shown in FIG. 5A. Because there is a plurality of cellshaving the poor BCMCS reception capability, only the cells with the poorreception capability and their neighbor cells transmit again the samedata at the next 4th slot according to the 4-slot interlacing scheme, orretransmit the same data using another interlacing scheme. As a result,the number of cells 510 and 540 with the poor BCMCS reception capabilitynoticeably decreases as shown in FIG. 5B. This is because mobilestations can increase decoding success rates by IR-combining the datareceived over two times.

If only the cells with the poor reception capability and their neighborcells perform third transmission in the next 4th slot according to the4-slot interlacing scheme, there is no cell with the poor receptioncapability as shown in FIG. 5C. If the retransmissions are performed inthis manner, the number of base stations that should provide BCMCS atthe time after the initial transmission decreases. As a result, from thesecond transmission, the ISI can be reduced even though the length ofthe CP is reduced. Therefore, from the second transmission, the cellscan increase the reception success rate even though they transmit thedata in a format different from that used for initial transmission,making it possible to freely vary a length of the CP.

FIG. 6 is a block diagram illustrating a structure of a base station'stransmitter for transmitting BCMCS traffic according to an exemplaryembodiment of the present invention. The transmitter of FIG. 6 includesa transmission unit for generating an OFDM symbol using a broadcastphysical layer packet, in other words broadcast traffic, according to anEBCMC transmission format proposed in an exemplary embodiment of thepresent invention, a radio frequency (RF) unit forfrequency-up-converting the broadcast traffic based on the EBCMCtransmission format into an RF signal for a slot interval beforetransmission, and a controller for controlling generation of the OFDMsymbol based on the EBCMC transmission format and controlling operationsof the transmission unit and the RF unit such that during initialtransmission and retransmission operations, the broadcast traffics aretransmitted for the corresponding slot intervals.

A controller 631 controls the overall operation of the base station. Inparticular, according to an exemplary embodiment of the presentinvention, the controller 631 receives a format index and a packet sizebased on the number of transmissions and information on the maximumnumber of transmission slots from an upper node (not shown) or ascheduler (also not shown) during BCMCS traffic transmission. Thecontroller 631 controls each of the blocks shown in FIG. 6 based on thereceived information. That is, the controller 631 controls a coding rateof an encoder 627, controls an interleaving process of an interleaver625 and a transmission block size of a transmission block generator 621,controls a modulation of a modulator 619, controls a guard tone to beinserted by a guard tone inserter 617, controls pilot tone insertionperformed in a pilot tone inserter 615, controls inverse fast Fouriertransform (IFFT) performed in an IFFT processor 613, and controls CPinsertion preformed in a CP inserter 611.

In FIG. 6, a memory 629 can generally have a queue as an area fortemporarily storing the transmission data received from an upper layer,or can be implemented in the form of a buffer. The memory 629 has areasfor storing data of their associated services, and performs a functionof temporarily storing transmission data until a transmission timearrives by a scheduler (not shown). If the transmission time arrives bythe scheduler, the data stored in the memory 629 for each individualservice or individual user is output to the encoder 627 according to acontrol signal output from the controller 631.

The encoder 627 channel-encodes the data received from the memory 629under the control of the controller 631. The typical channel encodingapparatus includes a turbo encoder, and can vary a coding rate accordingto a packet size. The signal output from the encoder 627 is input to theinterleaver 625. The interleaver 625 interleaves the coded symbolsaccording to packet size information received from the controller 631.The interleaving is a process of permuting the coded symbols in order toprevent a burst error of the channel. The interleaved symbols aretemporarily stored in the memory 623 on a packet-by-packet basis. Thetransmission block generator 621 generates transmission blocks byextracting the packets temporarily stored in the memory 623 bit by bitat a transmission time, in other words at the current transmission slot.The transmission blocks extracted by the transmission block generator621 are input to the modulator 619. The modulator 619 modulates theinput coded bits according to the modulation order information receivedfrom the controller 631.

The bits modulated by the modulator 619 are input to the guard toneinserter 617. The guard tone inserter 617, under the control of thecontroller 631, acquires the number and positions of the guard tones tobe inserted, inserts the guard tones between the modulation symbols, andoutputs the guard tone-inserted symbols to the pilot tone inserter 615.The pilot tone inserter 615 receives the number and positions of pilottones, a PDR, and dual PDR setting information from the controller 613,inserts the transmission pilot tones at the PDR, and outputs the pilottone-inserted symbols to the IFFT processor 613. The pilot tone inserter615 can change the PDR according to an EBCMC transmission format or atransmission slot number. The IFFT processor 613 performs IFFT accordingto an FFT size value received from the controller 631. TheIFFT-processed symbols are input to the CP inserter 611. The CP inserter611 generates an OFDM symbol by copying the CP, a length of which isdifferently set according to the number of transmissions by thecontroller 631.

The generated OFDM symbols are up-converted (not shown) to atransmission band, and then transmitted over a radio channel via anantenna ANT.

FIG. 7 is a block diagram illustrating an internal structure of areceiver for receiving an OFDM symbol according to an exemplaryembodiment of the present invention. The receiver of FIG. 7 includes anundepicted RF unit for frequency-down-converting received broadcasttraffic, in other words a broadcast physical layer packet, a receptionunit for receiving the broadcast physical layer packet according to atransmission format of the corresponding slot thereby restoring thereceived packet to its original signal, and a controller for controllingoperations of the RF unit and the reception unit such that duringinitial transmission and retransmission operations, the broadcastphysical layer packets are received according to the corresponding slotintervals.

In FIG. 7, a controller 731 controls the overall operation of thereceiver, and in particular, performs an operation necessary forreceiving OFDM symbols according to an exemplary embodiment of thepresent invention. Because the OFDM symbols according to an exemplaryembodiment of the present invention use the 4-slot interlacing schemefor the HRPD system, the controller 731 receives the OFDM symbols atintervals of 4 slots, and extracts 4 OFDM symbols at one slot asdescribed in connection with FIG. 4. In addition, because the length ofthe CP in the OFDM symbol can be differently set according to the numberof transmissions, the controller 731 determines the CP length from thebroadcast overhead message and performs a control operation forrestoring the data according to the CP length. That is, when aparticular BCMCS is received in a particular format, the controller 731controls the other constituent elements so that an OFDM signal receiveddepending on a format index, a packet size and the maximum number oftransmission slots is received as an OFDM symbol corresponding to theBCMC transmission format.

A CP remover 711 removes a CP contaminated by ISI from the received OFDMsymbol based on the information received from the controller 731. TheCP-removed OFDM symbol is input to a fast Fourier transform (FFT)processor 713. The FFT processor 713 performs an inverse process of theIFFT according to FFT size information received from the controller 731.The FFT-processed signal is branched into two paths as shown in FIG. 7,and input to a channel estimator 717 and a channel compensator 715. Thechannel estimator 717 extracts a pilot tone from the FFT-processed OFDMsymbol and generates a channel estimation value for compensation of atraffic symbol. For the channel estimation, the channel estimator 717receives the number and positions of pilot tones, the number andpositions of guard tones, and a PDR value from the controller 731. Thechannel compensator 715 performs channel compensation on the trafficsymbols received from the FFT processor 713 using the channel estimationvalue received from the channel estimator 717.

The channel-compensated symbols are input to a demodulator 719. Thedemodulator 719 demodulates the signal modulated in the transmitteraccording to the information on a modulation order acquired from thecontroller 731, and inputs the demodulated signal to a buffer 721. Thebuffer 721 stores Log likely hood (LLR) values of the demodulatedsignal. When the data is transmitted through multiple slots as describedin an exemplary embodiment of the present invention, the buffer 721stores the data transmitted through a plurality of sub-packets.Therefore, if decoding of one packet is completed, all values stored inthe buffer 721 should be reset to ‘0’. After a particular slot isreceived, the data stored in the buffer 721 is output to a deinterleaver723. The deinterleaver 723, a channel deinterleaver, performsdeinterleaving according to a unique number of the currently transmittedslot and a unit number of a block, received from the controller 731. Thedeinterleaving is a process of performing an inverse process of theinterleaving performed in the transmitter during transmission. That is,the deinterleaving is a process of inversely permuting the permutedbits. The signals deinterleaved in the deinterleaver 723 are input to adecoder 725. The decoder 725 decodes the deinterleaved signals andoutputs information bits. In this case, for the unicast data, thedecoder 725 outputs a decoding error result to the controller 731,because the controller 731 should receive the decoding error result inorder to request retransmission. Even for the BCMCS, the decoder 725 cantransmit the decoding error result so that the controller 731 mayperform an error correction operation.

A description will now be made of an operation performed in each of theelements during transmission of BCMCS according to an exemplaryembodiment of the present invention.

FIG. 8 is a flowchart illustrating a process of transmitting broadcastservice traffic in a base station according to an exemplary embodimentof the present invention.

Before a description of FIG. 8 is given, it should be noted that theexemplary process of FIG. 8 is performed for traffic of each broadcastservice. In addition, it is assumed that the base station receivesbroadcast service traffic from an upper layer and broadcasts thereceived broadcast service traffic to mobile stations. In step 800, thebase station sets a value N indicating a unique number of the currenttransmission packet, in other words the number of transmissions, to ‘1’for a corresponding broadcast service. Thereafter, in step 802, the basestation determines whether N=1. After initially setting the value N, thebase station may skip step 802. For convenience, however, it will beassumed herein that the base station performs step 802. If it isdetermined in step 802 that N=1, the base station proceeds to step 808.Otherwise, the base station proceeds to step 804. In step 808, the basestation generates an OFDM symbol using packet data in a formatassociated with the value N, and transmits the OFDM symbol for one slot.This control operation will be described in detail hereinbelow withreference to the accompanying tables. After transmitting the packet datain this way, the base station increases the value N by 1 in step 810,and returns to step 802.

In step 804, the base station determines whether the value N is lessthan or equal to a maximum value. The maximum value indicates a maximumnumber of transmissions. For example, if the maximum number oftransmissions is 3, the maximum value is 3. If the value N is greaterthan the maximum value, indicating that the base station increased thevalue N by 1 in step 810 after the value N reached the maximum number oftransmissions, then the base station sets the value N to ‘1’ in step806, and then proceeds to step 808. However, if the value N is notgreater than the value maximum value, the base station transmits packetdata in a format associated with the corresponding number N oftransmissions in step 808. For example, the base station performsinitial transmission on the OFDM symbol for N=1, performs firstretransmission for N=2, and performs second retransmission for N=3.

A broadcast overhead message transmitted by the base station is notshown in FIG. 8. For the overhead, the base station generates andtransmits the broadcast overhead message at certain intervals. Thebroadcast overhead message, as described above, includes information onthe configuration format of the OFDM symbol. The format information canbe defined as a length of a CP, the number of valid chips, the number ofpilot tones, the number of guard tones, a PDR, a dual PDR setting value,a modulation order, and the like.

FIG. 9 is a flowchart illustrating a process of receiving broadcastservice traffic in a mobile station according to an exemplary embodimentof the present invention.

Before a description of FIG. 9 is given, the prerequisites in the mobilestation will be described. A user of the mobile station should desire toreceive a broadcast service, and the mobile station should have receiveda broadcast overhead message periodically transmitted from a basestation and acquired information on the desired broadcast traffic. Inaddition, the mobile station has already passed the authentication andregistration processes, if necessary to receive the initial broadcastservice. Through this process, the mobile station extracts informationon the desired broadcast service from the received broadcast overheadmessage. The extracted information includes a BCMC flow ID for thebroadcast service desired by the user, a transfer rate of the channelover which the desired broadcast service is transmitted, information onthe physical channel constituting a logical channel over which thebroadcast service is transmitted, a format index, and the number ofbroadcast transmission slots. Based on the format index, the mobilestation can be aware of an OFDM symbol configuration and a modulationorder, defined between the mobile station and the base station.Thereafter, the mobile station checks the broadcast overhead messageevery slot.

A description will now be made of an operation of the mobile stationaccording to an exemplary embodiment of the present invention in thestate where the prerequisites are satisfied. In step 900, the mobilestation determines whether the current slot is a slot for receivingdesired broadcast service. If the current slot is a slot for receivingthe desired broadcast signals, the mobile station proceeds to step 904.Otherwise, the mobile station proceeds to step 902 where it performs anoperation of handling a received message.

The received message handling mode includes the process of receiving thebroadcast overhead message. In step 904, the mobile station calculatesthe order of the current reception slot, in other words determines thenumber of transmissions for the current reception slot. Aftercalculating the number of transmissions for the current reception slot,the mobile station receives OFDM symbols according to a format of thecurrent slot in step 906. For example, if the number of transmissionsfor the currently received slot is M, the mobile station interprets thereceived signal as an OFDM symbol in the format associated with Mthreception, performing a reception process. Then the mobile stationperforms channel estimation using a PDR mapped to the Mth receptionformat. Thereafter, the mobile station performs demodulation accordingto a modulation order mapped to the Mth reception format. In step 908,the mobile station stores the received data in an area of a buffer 721shown in FIG. 7. The mobile station stores the demodulated symbol in thearea corresponding to an Mth slot for the current packet in the buffer721. Thereafter, in step 910, the mobile station determines whether thenumber of receptions has reached the maximum number of transmissions, asdetermined in the system. If it is determined that the number ofreceptions has reached the maximum number of transmissions, the mobilestation decodes the data stored in the buffer 721 in step 912. However,if the number of receptions has not reached the maximum number oftransmissions, the mobile station waits until the number of receptionsreaches the maximum number of transmissions. It should be noted that themobile station, depending on its structure, may attempt the decodingeven before the number of receptions reaches the maximum value. If themobile station fails in decoding, it receives sub-packets in the nextbroadcast transmission slot and then stores the received sub-packets inthe corresponding area of the buffer 721. Thereafter, the mobile stationmay reattempt the decoding.

A detailed description will now be made of a method for transmittingbroadcast data in a different OFDM format according to the number oftransmissions according to an exemplary embodiment of the presentinvention.

Herein, a detailed description will be made of a method for defining asignal transmission format in the system using a plurality of the OFDMsignal transmission formats. The constituent elements of thetransmission format according to an exemplary embodiment of the presentinvention, as described above, can include a modulator order and a PDRvalue. The PDR value can be set depending on whether each of 4 OFDMsymbols transmitted in one slot is an internal symbol (for example, 2ndand 3rd symbols in FIG. 4) or a boundary symbol (for examples, 1st and4st symbols in FIG. 4).

Generally, a Single Frequency Network (SFN)-based OFDM broadcast system(including a broadcast system based on a communication system) sets alength of a CP of an OFDM symbol relatively long in order to obtain anSFN gain. As described above, the CP is a signal attached to the head ofan OFDM symbol, and the CP interval is a signal interval provided forsuppressing the ISI which may occur when a receiver receives multi-pathsignals. An OFDM symbol that arrives after being delayed for a timelonger than the CP interval on the basis of the signal first received atthe receiver causes ISI in the receiver, reducing reception capability.Therefore, the SFN communication system with a long propagation delaysets the guard interval, in other words the CP, relatively long so as tosuppress interference and make strength of the signal high enough, ifpossible. This is applied even to the BCMCS provided in the CDMA2000HRPD system. In the CDMA2000 HRPD system, cells in a particular areatransmit the same broadcast signals, and the receiver preferablycombines as many received signals as possible to reduce interference andimprove reception quality. Therefore, the system sets the CP interval ofthe OFDM symbol long as described above.

However, because a cell located in a boundary with another broadcastarea, or a cell located in shadow area decreases in reception rate withthe single transmission, it retransmits a BCMC packet using a unicastslot in order to compensate for the decrease in the reception rate.Generally, the retransmission is performed only in the area with thepoor reception environment. The decrease in the cell area where the samesignals are transmitted reduces a delay time of the signals arriving atthe receiver, making it unnecessary to set the CP interval of the OFDMsymbol long. That is, it is not possible to obtain the SFN gain at theretransmission time. If retransmission may occur in a particular celltwo times or more, the signal delay time may decrease because theincrease in the number of retransmissions decreases the number of thecells where the retransmission occurs. That is, as described above, ifthe retransmissions continuously occur as described in connection withFIGS. 5A to 5C, the number of the cells where the retransmissions areperformed decreases each time the retransmission occurs.

Taking into account the fact that the broadcast reception characteristicchanges during retransmission, it is possible to change a format of theOFDM signal according to a reception environment during theretransmission. That is, it is possible to increase a ratio of datasymbols by reducing a length of the CP interval during theretransmission, contributing to a decrease in the coding rate andimprovement in the reception capability.

Table 1 below shows a possible exemplary format of a transmission OFDMsymbol.

TABLE 1 Symbol Symbol Symbol Configuration 0 Configuration 1Configuration 2 Guard interval (CP) 80 40 16 (chip) Valid data (chip)320 360 384 Number of pilot tones 64 36 24 Number of guard tones 20 0 0

It would be obvious to those skilled in the art that the transmissionformat is subject to change. In Table 1, a format with a longer lengthof the CP permits a longer multi-path delay. The use of the format withthe long length of the CP obtains a higher SFN gain. On the contrary,the use of a format with a short length of the CP contributes to anincrease in data throughput. The terms used in Table 1 will be definedhereinbelow.

(1) CP interval (or Guard interval): It indicates the number of chipsavailable in a CP interval in one OFDM symbol inserted into a ½ slot inan HRPD system.

(2) Valid data: It indicates the number of chips available for datatransmission except for the guard interval, in other words the CPinterval, in one OFDM symbol inserted into a ½ slot in the HRPD system.

(3) Number of pilot tones: It indicates the number of pilot tonesinserted in a valid data interval in one OFDM symbol inserted into a ½slot in the HRPD system.

(4) Number of Guard tones: It indicates the number of guard tonesinserted in a valid data interval in one OFDM symbol inserted into a ½slot in the HRPD system.

FIG. 10 is a timing diagram illustrating a scenario in which tworetransmissions are performed in a 4-slot interlacing scheme accordingto another exemplary embodiment of the present invention. In thescenario of FIG. 10, Packet #1, Packet #2, Packet #3 and Packet #4constituting one encoder packet are retransmitted two times, and notransmission is performed in an adjacent time slot. It can be noted thattime slots 1001 and 1003 where the Packet #1 and Packet #2 aretransmitted, and time slots 1002 and 1004 where unicast transmission isperformed adopt the 4-slot interlacing scheme. Therefore, at initialtransmission of the Packet #1 and Packet #2, an OFDM symbol of a symbolconfiguration-0 type is 16 QAM-modulated before being transmitted, andin time slots 1011 and 1013 for second transmission, in other wordsfirst retransmission, slots 1012 and 1014 where unicast transmission isperformed even for second transmission are transmitted in the samemethod. At the last third transmission, in other words secondretransmission, an OFDM symbol of a symbol configuration-1 type isQPSK-modulated before being transmitted, unlike in the initialtransmission. After the 3 transmissions are all completed using thesymbol configuration and modulation methods corresponding to the orderof the transmission slots, the next packet is transmitted. That is, theintervals where initial transmissions of the Packet #3 and Packet #4 areperformed are represented by reference numerals 1031 and 1033.

In the exemplary scenario of FIG. 10, the method of transmitting onepacket by a base station includes the following elements:

(1) Encoder packet size

(2) Span (or Number of transmission slots)

(3) per-slot OFDM symbol configuration (or OFDM symbol configuration pertransmission slot)

(4) per-slot Modulation order (or Modulation order per transmissionslot)

(5) per-PDR (or PDR per transmission slot)

In order to simply represent this packet transmission scheme, theper-slot OFDM symbol configuration and the per-slot modulation orderamong the above elements will be represented in one format. When only 3types of symbol configurations and 2 types of modulation orders aretaken into consideration, a total of 6 combinations are possible asshown in Table 2 below, and the 6 possible combinations are named asFormat A to Format F, respectively. The number of the possibleconfigurations is extensible according to the number of symbolconfigurations and the number of modulation orders.

TABLE 2 Combination of OFDM symbol configuration and Modulation orderFormat name Symbol Configuration 0, 16QAM A Symbol Configuration 1,16QAM B Symbol Configuration 2, 16QAM C Symbol Configuration 0, QPSK DSymbol Configuration 1, QPSK E Symbol Configuration 2, QPSK F

In order to effectively apply an exemplary embodiment of the presentinvention, the base station needs to previously define the appropriatenumber of slots, and transmission formats for the individual slots(per-slot transmission formats) according to the environments, andprovide information on the number of slots and the per-slot transmissionformats to the mobile station using an appropriate method.Alternatively, the mobile station may previously have the information onthe number of slots and the per-slot transmission formats. It will beassumed herein that an agreement between the mobile station and the basestation is made such that the number of slots and the per-slottransmission formats are represented by format index values.

When a combination of an OFDM symbol configuration and a modulationorder is defined as one format as shown in Table 2, there are variouspossible transmission methods (span and transmission formats) defined inTable 3 below. Although there are various possible transmission formatcombinations, the transmission format combinations of Table 3 satisfythe following two conditions:

(A) An increase in the number of transmissions maintains or decreasesthe modulation order.

(B) An increase in the number of transmissions maintains or increasesthe number of valid data chips.

The above two conditions are the results that can be obtained by takinginto account the fact that the increase in the number of retransmissionsdecreases the number of areas where the BCMC signals are transmitted.

Table 3 below shows which transmission format the system that performs 3transmissions will use for each individual slot. Each case can berepresented with a number indicating a format index. For example, aformat index value ‘1’ indicates that three slots are transmitted in atransmission format A, a transmission format B, and a transmissionformat C, respectively.

TABLE 3 First Format Initial retrans- Second index Modulation ordertransmission mission retransmission 0 initial transmission: A A A 116QAM A A B 2 first retransmission: A A C 3 16QAM A B B 4 secondretransmission: A B C 5 16QAM A C C 6 B B B 7 B B C 8 B C C 9 C C C 10initial transmission: A A D 11 16QAM A A E 12 first retransmission: A AF 13 16QAM A B E 14 second retransmission: A B F 15 QPSK A C F 16 B B E17 B B F 18 B C F 19 C C F 20 initial transmission: A D D 21 16QAM A D E22 first retransmission: A D F 23 QPSK B E E 24 second retransmission: BE F 25 QPSK B F F 26 C F F

When the per-slot transmission formats are defined as shown in Table 3,the base station can provide information indicating a broadcast type anda transmission format used in the corresponding area to the mobilestation simply with the format index using, for example, a broadcastoverhead message. For the case where less then three slots aretransmitted, the base station needs to provide the mobile station withthe span and the format index together. Alternatively, it is alsopossible to bind these two parameters, in other words the span and theformat index, into one parameter, and express the one parameter as anEBCMC transmission format.

As an exemplary alternative method, the base station may provide onlythe format index to the mobile station. That is, even though the basestation does not provide the span (in other words the total number oftransmission slots), the mobile station can perform decoding byattempting the decoding taking all possible cases into account. The basestation can provide only the format index, and spontaneously determinethe actual span. If the actual span is less than the span determinedthrough the format index, the base station may transmit unicast packetsfor the remaining slots.

A possible format of the broadcast overhead message for the use of theabove method is shown in Table 4.

TABLE 4 Field Length(bits) [ . . . ] [ . . . ] NeighborCount 5 [ . . . ][ . . . ] NumExtendedSlotIncluded 1 [ . . . ] [ . . . ] BCMCSFlowCount NBCMCSFlowCount occurrence of the following variable length record:{BCMCSFlowID 4 [ . . . ] [ . . . ] NumExtendedSlot 0 or 2 FormatIndex 0or 5 [ . . . ] [ . . . ] Zero or NeighborCount occurrences of thefollowing fields [ . . . ] [ . . . ] NumExtendedSlot 0 or 2 FormatIndex0 or 5 [ . . . ] [ . . . ]    } [ . . . ] [ . . . ]

The message of Table 4 indicates whether to additionally transmit apacket for each individual BCMCS flow, and in this case, it is possibleto provide a per-slot transmission format using an OFDM format index. Inaddition, in order to provide transmission information in a neighborcell, the message indicates whether to additionally transmit a packet inthe neighbor cell in the same way, and in this case, it provides theper-slot transmission format using a FormatIndex field. The fields inTable 4 are used for the following purposes.

(1) NeighborCount: It indicates the number of neighbor cells, containingbroadcast transmission information included in this message.

(2) NumExtendedSlotIncluded: It is an indicator indicating whether thereare any included fields indicating additional transmission in additionto the determined transmission slot and transmission method. While thedetermined transmission slot and transmission method are applied in thesame way to all neighbor cells included in this message, the informationincluded by this indicator can be different for each cell.

(3) BCMCSFlowCount: It indicates the number of BCMCS flows included inthis message.

(4) BCMCSFlowID: It is an identifier of a corresponding broadcastservice.

(5) NumExtendedSlot: It indicates the number of slots which areadditionally transmitted packet by packet, and this field is includedonly when “NumExtendedSlotIncluded” is ‘1’ in Table 4.

(6) FormatIndex: It indicates a transmission format used fortransmission. This field is included only whenNumExtendedSlotIncluded=‘1’ and NumExtendedSlot=‘0’ in Table 4.

Table 3 above shows possible combinations of transmission formatsaccording to an exemplary embodiment of the present invention. In theactual mobile communication system, it is possible to selectively useonly some of the transmission formats shown in Table 3 in order tosimplify the system design and verification.

Table 5 to Table 8 below show possible exemplary combinations in thecase where only some of all possible combinations are selectively used.That is, embodiments of Table 5 to Table 8 define different OFDM symbolformats/per-slot modulation orders for individual packetsizes/transmission slots, and regard all of the OFDM symbolformats/per-slot modulation orders as one transmission formatcombination. This transmission format combination will be defined as amode. That is, the base station/mobile station uses thetransmission/reception packet size, the OFDM symbol corresponding to theslot, and the modulation order, for transmission (by basestation)/reception (by base station).

TABLE 5 Packet Tx1 Tx2 Tx3 Tx4 Tx1 Tx2 Tx3 Tx4 Size OFDM OFDM OFDM OFDMModulation Modulation Modulation Modulation 2048 320 320 320 — 16QAM16QAM 16QAM — tone tone tone 3072 320 320 320 — 16QAM 16QAM 16QAM — tonetone tone 5120 320 320 320 320 16QAM 16QAM 16QAM 16QAM tone tone tonetone 3072 360 360 360 — 16QAM 16QAM 16QAM — tone tone tone 4096 360 360360 — 16QAM 16QAM 16QAM — tone tone tone

Table 5 above shows an exemplary transmission format for a default modeor fixed mode. In Table 5, for the packet sizes of 2048, 3072, 4096, and5120, initial transmission and its succeeding transmissions have thesame modulation order (or modulation scheme) and the same OFDM format.Transmission for the mode specified in Table 5 is configured based onthe conventional technology to which the present invention is notapplied.

TABLE 6 Packet Tx1 Tx2 Tx3 Tx4 Tx1 Tx2 Tx3 Tx4 Size OFDM OFDM OFDM OFDMModulation Modulation Modulation Modulation 2048 320 360 360 — 16QAMQPSK QPSK — tone tone tone 3072 320 360 360 — 16QAM QPSK QPSK — tonetone tone 5120 320 320 360 360 16QAM 16QAM QPSK QPSK tone tone tone tone3072 360 384 384 — 16QAM QPSK QPSK — tone tone tone 4096 360 384 384 —16QAM QPSK QPSK — tone tone tone

Table 6 above shows a transmission format of a zone-based modeconfigured according to an exemplary embodiment of the presentinvention. The transmission format of Table 6 is determined based on thefollowing criteria.

(1) The modulation order and the OFDM format associated with atransmission format are used for the transmissions until a channelcoding rate≦1.

(2) The OFDM format changes step by step from the transmission after thechannel coding rate<1. For example, the OFDM format changes from 320tones to 360 tones, and from 360 tones to 384 tones step by step.

(3) When the OFDM format changes as stated in (2), 16 QAM also changesto QPSK.

TABLE 7 Packet Tx1 Tx2 Tx3 Tx4 Tx1 Tx2 Tx3 Tx4 Size OFDM OFDM OFDM OFDMModulation Modulation Modulation Modulation 2048 320 360 360 — 16QAMQPSK QPSK — tone tone tone 3072 320 360 360 — 16QAM QPSK QPSK — tonetone tone 5120 320 320 320 360 16QAM 16QAM 16QAM QPSK tone tone tonetone 3072 360 384 384 — 16QAM QPSK QPSK — tone tone tone 4096 360 360384 — 16QAM 16QAM QPSK — tone tone tone

Table 7 above shows another transmission format of a zone-based modeconfigured according to an exemplary embodiment of the presentinvention. The transmission format of Table 7 is determined based on thefollowing criteria.

(1) On the assumption that one transmission is performed in a 1.6667 mstransmission interval, a transmission format associated with apredetermined mode is used at a data rate higher than a reference rateof 1 Mbps. The OFDM format changes step by step as described in Table 6,at a data rate lower than the reference rate.

(2) When the OFDM format changes as stated in (1), 16 QAM also changesto QPSK.

As an exemplary application of the criteria used for determining thetransmission format of Table 7, for second transmission for 2048 bits,because a data rate is 614.4 kbps (=2048/(1.6667 ms*2)), the 360-toneOFDM format and QPSK modulation are used from the second transmission.It determines whether to change the transmission format of Table 7 in amode on the basis of a particular data rate of 1 Mbps. It would beobvious to those skilled in the art that this scheme can be applied inthe same way even though another data rate is used.

TABLE 8 Packet Tx1 Tx2 Tx3 Tx4 Tx1 Tx2 Tx3 Tx4 Size OFDM OFDM OFDM OFDMModulation Modulation Modulation Modulation 2048 320 320 360 — 16QAM16QAM QPSK — tone tone tone 3072 320 320 360 — 16QAM 16QAM QPSK — tonetone tone 5120 320 320 320 360 16QAM 16QAM 16QAM QPSK tone tone tonetone 3072 360 360 384 — 16QAM 16QAM QPSK — tone tone tone 4096 360 360384 — 16QAM 16QAM QPSK — tone tone tone

Table 8 above shows an exemplary transmission format of a zone-basedmode configured according to another exemplary embodiment of the presentinvention. The transmission format of Table 8 is determined based on thefollowing criteria.

(1) At the last transmission, the OFDM format always changes step bystep. For example, the OFDM format changes from 320 tones to 360 tones,and from 360 tones to 384 tones.

(2) When the OFDM format changes, 16 QAM also changes to QPSK.

TABLE 9 Packet Tx1 Tx2 Tx3 Tx4 Tx1 Tx2 Tx3 Tx4 Size OFDM OFDM OFDM OFDMModulation Modulation Modulation Modulation 2048 320 360 360 — 16QAM16QAM 16QAM — tone tone tone 3072 320 360 360 — 16QAM 16QAM 16QAM — tonetone tone 5120 320 320 360 360 16QAM 16QAM 16QAM 16QAM tone tone tonetone 3072 360 384 384 — 16QAM 16QAM 16QAM — tone tone tone 4096 360 384384 — 16QAM 16QAM 16QAM — tone tone tone

Table 9 above shows an exemplary transmission format of a zone-basedmode configured according to further another exemplary embodiment of thepresent invention. The transmission format of Table 9 is determinedbased on the following criterion.

(1) The modulation order and the OFDM format associated with atransmission format are used for the transmissions until a channelcoding rate≦1.

The mobile communication system basically supports the transmissionformat for the mode, shown in Table 5, and can additionally support oneof the transmission formats of the zone-based mode, shown in Table 6 toTable 9. Therefore, each mode can be indexed with a transmission formatindex as shown in Table 3, and then transmitted from the base station tothe mobile station through a signaling message or a broadcast overheadmessage. In this case, the corresponding field can be named as a modeindex. Because the mobile station can directly or indirectly providesize information of the packet the base station will transmit, using afield other than the mode index, the mobile station can determine a slotand an OFDM format to be used for reception, using the mode index andpacket size information of the current broadcast service. The reductionin types of the supported transmission formats contributes to simplerealization of the mobile communication system's transceiver.

TABLE 10 Number of Number of Physical Tones for Tones for LayerEBCMCSTransmissionFormat Data Rate Span1 Span2 Packet Size Span1 Span2field (kbps) (N_(FFT1)) (N_(FFT2)) (bits) (slots) (slots) ‘000000’1843.2 320 NA 3072 1 NA ‘000001’ 921.6 320 NA 3072 2 NA ‘000010’ 614.4320 NA 3072 3 NA ‘000100’ 1228.8 320 NA 2048 1 NA ‘000101’ 614.4 320 NA2048 2 NA ‘000110’ 409.6 320 NA 2048 3 NA ‘001001’ 1536.0 320 NA 5120 2NA ‘001010’ 1024.0 320 NA 5120 3 NA ‘001011’ 768.0 320 NA 5120 4 NA‘001100’ 2457.7 360 NA 4096 1 NA ‘001101’ 1228.8 360 NA 4096 2 NA‘001110’ 819.2 360 NA 4096 3 NA ‘010000’ 1843.2 360 NA 3072 1 NA‘010001’ 921.6 360 NA 3072 2 NA ‘010010’ 614.4 360 NA 3072 3 NA ‘100001’921.6 320 360 3072 1 1 ‘100010’ 614.4 320 360 3072 1 2 ‘100101’ 614.4320 360 2048 1 1 ‘100110’ 409.6 320 360 2048 1 2 ‘101010’ 1024.0 320 3605120 2 1 ‘101011’ 768.0 320 360 5120 2 2 ‘101101’ 1228.8 360 384 4096 11 ‘101110’ 819.2 360 384 4096 1 2 ‘110001’ 921.6 360 384 3072 1 1‘110010’ 614.4 360 384 3072 1 2 All other Reserved settings

Table 10 above expresses a combination of the mode index, the encoderpacket size, and the span, mentioned in Table 9, as an indexEBCMCSTransmissionFormat.

Table 10 shows one mode made by combining the modes presented in Table 5and Table 9. The most significant bit (MSB) of theEBCMCSTransmissionFormat serves as a mode index. That is, for MSB=0, thetransmitter continues transmission without changing the OFDM symbolformat, and for MSB=1, the transmitter operates in the mode mentioned inTable 9. In other words, MSB=1 indicates a mode in which the OFDM symbolformat changes from a second slot (for Encoder Packet size=2048, 3072,and 4096) or a third slot (for Encoder Packet size=5120).

“Number of Tones for Span 1” indicates the number of OFDM format tonesused in the interval where the OFDM symbol format is not changed, and“Number of Tones for Span 2” indicates the number of OFDM format tonesused in the interval where the OFDM symbol format is changed. “PhysicalLayer packet size” indicates a size of an encoder packet. “Span1” and“Span2” indicate the number of slots where the OFDM symbol format is notchanged, and the number of slots where the OFDM symbol format ischanged, respectively. As shown in Table 9, the format change occursonly once regardless of whether the maximum span is 3 slots or 4 slots.

Next, a description will be made as to how the proposed indexing methodcan be applied to the broadcast overhead message. A message shown inTable 11 below is configured such that PDRs of 0th and 3rd OFDM blockscan be set different from PDRs of 1st and 2nd OFDM blocks. Table 11 alsopresents an exemplary method for setting a dual PDR in the case where avariable format is applied.

TABLE 11 DualPDREnabled 1 BCMCSFlowCount 7 BCMCSFlowCount occurrences ofthe following variable-length record: BCMCSFlowID (BCMCSFlowIDLength + 1) × 8 [ . . . ] LogicalChannelSameAsPreviousBCMCSFlow 1 Zeroor one occurrence of the following nine field recordPhysicalChannelCount 7 EBCMCSTransmissionFormat 0 or 6 [ . . . ]DCPilotToDataGain 0 or 5 DualPDREnabledForThisLogicalChannel 0 or 1ACPilotToDataGainRecord 0, 5, 10, x or y Period 0 or 3 Zero orPhysicalChannelCount occurrences of the following two fields: Interlace2 Multiplex 4 AdditionalCDMAChannelsSameAsPrevious 1 BCMCSFlowAdditionalCDMAChannelCount 0 or 3 Zero or AdditionalCDMAChannelCountoccurrences of the following field AdditionalCDMAChannel 24 

A description will now be made of the fields shown in Table 11.

(1) DualPDREnabled: An access network, in other words a base station ora base station controller, sets this field to ‘1’ if it uses a dualpilot-to-data gain. Otherwise, the access network sets this field to‘0’.

(2) BCMCSFlowCount: It indicates the number of BCMCS Flow identifiersincluded in the message of Table 11 transmitted by the access network.

(3) BCMCSFlowID: It is set by the access network, and is set as a BCMCSFlow identifier of a particular BCMC flow.

(4) LogicalChannelSameAsPreviousBCMCSFlow: If this BCMC Flow istransmitted through the same logical channel as that of the previousBCMC Flow recorded in this message, the access network sets this fieldto ‘1’. Otherwise, the access network sets this field to ‘0’.

(5) PhysicalChannelCount: If the LogicalChannelSameAsPreviousBCMCSFlowdescribed in (4) is set to ‘1’, the access network omits this field.Otherwise, this field sets the number of interlace-multiplex pairsconstituting a logical channel within the range of 0 to 64.

(6) EBCMCSTransmissionFormat: If theLogicalChannelSameAsPreviousBCMCSFlow described in (4) is set to ‘1’, orif the PhysicalChannelCount described in (5) is set to ‘0’, the accessnetwork will omit this field. Otherwise, the access network sets anEnhanced Broadcast transmission format used for transmitting thislogical channel in accordance with Table 10 above.

(7) DCPilotToDataGain: If the LogicalChannelSameAs-PreviousBCMCSFlowdescribed in (4) is set to ‘1’, or if the PhysicalChannelCount describedin (5) is set to ‘0’, this field is omitted. Otherwise, the accessnetwork will set this field to a power ratio of a zero frequency's pilottone to a non-zero frequency's data tone. If this field is set to‘10000’, this field value is construed as ‘0’ in a linear domain.Otherwise, this field value is construed as a 2's complement in 0.5-dBstep size.

(8) DualPDREnabledForThisLogicalChannel: If the DualPDREnabled is set to‘0’, or if the LogicalChannelSameAsPreviousBCMCSFlow described in (4) isset to ‘1’, or if the PhysicalChannelCount described in (5) is set to‘0’, then the access network omits this field. Otherwise, the accessnetwork sets this field as follows. That is, the access network setsthis field to ‘1’, if the dual PDR is used for this logical channel.Otherwise, the access network sets this field to ‘0’.

(9) ACPilotToDataGainRecord: If the DualPDREnabledForThisLogicalChanneldescribed in (8) is not included in this message, the access networkomits this field. Otherwise, the access network sets this field asfollows:

-   -   If the DualPDREnabledForThisLogicalChannel is set to ‘0’ and the        MSB of the EBCMCSTransmissionFormat described in (6) is set to        ‘0’, the access network sets this record as defined in Table 12        below.    -   If the DualPDREnabledForThisLogicalChannel described in (8) is        set to ‘0’ and the MSB of the EBCMCSTransmissionFormat described        in (6) is set to ‘1’, the access network sets this record as        defined in Table 13 below.    -   If the DualPDREnabledForThisLogicalChannel described in (8) is        set to ‘1’ and the MSB is set to ‘0’, the access network sets        this field as defined in Table 14 below.    -   If the DualPDREnabledForThisLogicalChannel is set to ‘1’ and the        MSB of the EBCMCSTransmissionFormat described in (6) is set to        ‘1’, the access network sets this record as defined in Table 15        below.

Now, the foregoing conditions will be defined in Table 12 to Table 15,and a description of the fields shown in Table 12 to Table 15 will bemade hereinbelow.

TABLE 12 Sub-Field Length (bits) ACPilotToDataGain 5

In Table 12, the access network sets the ACPilotToDataGain field to apower ratio of a non-zero frequency's pilot tone to a non-zerofrequency's data tone. This field can be expressed with a 2's complementin 0.5 dB steps.

TABLE 13 Sub-Field Length (bits) ACPilotToDataGain1 5 ACPilotToDataGain25

In Table 13, the access network sets the ACPilotToDataGain1 field to apower ratio of a non-zero frequency's pilot tone to a non-zerofrequency's data tone for a Span1's slot. This field can be expressedwith a 2's complement in 0.5 dB steps. In addition, the access networksets the ACPilotToDataGain2 field to a power ratio of a non-zerofrequency's pilot tone to a non-zero frequency's data tone for a Span2'sslot. This field can be expressed with a 2's complement in 0.5 dB steps.

TABLE 14 Sub-Field Length (bits) ACInternalPilotToDataGain xACBoundaryPilotToDataGain x

In Table 14, the access network sets the ACInternalPilotToDataGain fieldto a power ratio of a non-zero frequency's pilot tone and a non-zerofrequency's data tone for each of OFDM block 1 and OFDM block 2. Thisfield can be expressed with a 2's complement in 0.5 dB steps. Inaddition, the access network sets the ACBoundaryPilotToDataGain field toa power ratio of a non-zero frequency's pilot tone and a non-zerofrequency's data tone for each of OFDM block 0 and OFDM block 3. Thisfield can be expressed with a 2's complement in 0.5 dB steps.

TABLE 15 Sub-Field Length (bits) ACInternalPilotToDataGain1 xACBoundaryPilotToDataGain1 x ACInternalPilotToDataGain2 xACBoundaryPilotToDataGain2 x

In Table 15, the access network sets the ACInternalPilotToDataGain1field to a power ratio of a non-zero frequency's pilot tone to anon-zero frequency's data tone for each of OFDM block 1 and OFDM block 2for Span1. This field can be expressed with a 2's complement in 0.5 dBsteps.

The access network sets the ACBoundaryPilotToDataGain1 field to a powerratio of a non-zero frequency's pilot tone and a non-zero frequency'sdata tone for each of OFDM block 0 and OFDM block 3 for Span1. Thisfield can be expressed with a 2's complement in 0.5 dB steps.

The access network sets the ACInternalPilotToDataGain2 field to a powerratio of a non-zero frequency's pilot tone to a non-zero frequency'sdata tone for each of OFDM block 1 and OFDM block 2 for Span2. Thisfield can be expressed with a 2's complement in 0.5 dB steps.

Finally, the access network sets the ACBoundaryPilotToDataGain2 field toa power ratio of a non-zero frequency's pilot tone to a non-zerofrequency's data tone for each of OFDM block 0 and OFDM block 3 forSpan2. This field can be expressed with a 2's complement in 0.5 dBsteps.

As can be understood from the foregoing description, in transmittingbroadcast data, the mobile communication system changes transmissionformats for initial transmission and retransmissions, increasingefficiency of radio resources and facilitating transmission of thebroadcast data.

While the invention has been shown and described with reference to acertain preferred embodiment thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and the full scope of equivalentsthereof.

1. A method for transmitting a broadcast physical layer packet in amobile communication system supporting multi-slot transmission andhybrid Automatic Repeat Request (H-ARQ), the method comprising:transmitting, by a controller, the broadcast physical layer packetaccording to a first transmission format for at least one first slotinterval; and retransmitting, by the controller, the broadcast physicallayer packet for at least one second slot interval using a secondtransmission format different from the first transmission format used inthe first slot interval, wherein the first transmission format is afixed transmission format and the second transmission format is avariable transmission format, wherein transmitting and retransmittingthe broadcast physical layer packet respectively comprise transmittingand retransmitting through an Orthogonal Frequency Division Multiplexing(OFDM) symbol, and wherein the controller varies at least one of thenumber of data tones, the number of pilot tones, and the number of guardtones in the OFDM symbol in the second slot interval at eachretransmission.
 2. The method of claim 1, further comprising: varying acyclic prefix (CP) length of the OFDM symbol in the second slot intervalat each retransmission.
 3. The method of claim 2, further comprising:decreasing the CP length in proportion to an increase in the number ofthe retransmissions.
 4. The method of claim 1, further comprising:varying a modulation order of the OFDM symbol in the second slotinterval at each retransmission.
 5. The method of claim 4, furthercomprising: decreasing the modulation order in proportion to an increasein the number of the retransmissions.
 6. The method of claim 1, furthercomprising: broadcasting a broadcast overhead message comprisingtransmission format information applied to each of the first and secondslot intervals.
 7. The method of claim 1, further comprising: acquiring,by at least one of mobile stations receiving the broadcast physicallayer packet, a transmission format applied to each of the first andsecond slot intervals by performing signaling with a base station thattransmits the broadcast physical layer packet.
 8. The apparatus of claim1, wherein the mobile communication system is a High Rate Packet Data(HRPD) system that transmits the broadcast physical layer packetaccording to an OFDM transmission scheme.
 9. An apparatus fortransmitting a broadcast physical layer packet in a mobile communicationsystem supporting multi-slot transmission and hybrid Automatic RepeatRequest (H-ARQ), the apparatus comprising: a transmission unit forgenerating a broadcast physical layer packet such that initialtransmission and retransmission differ from each other in a transmissionformat; a radio frequency (RF) unit for converting the broadcastphysical layer packet generated in the transmission unit into a higherfrequency RF signal; and a controller for controlling operations of thetransmission unit and the RF unit so as to initially transmit thebroadcast physical layer packet according to a fixed transmission formatfor at least one first slot interval, and retransmit the broadcastphysical layer packet for at least one second slot interval using avariable transmission format different from the transmission format usedin the first slot interval, wherein transmitting and retransmitting thebroadcast physical layer packet respectively comprise transmitting, andretransmitting through an Orthogonal Frequency Division Multiplexing(OFDM) symbol, and wherein the controller varies at least one of thenumber of data tones, the number of pilot tones, and the number of guardtones in the OFDM symbol in the second slot interval at eachretransmission.
 10. The apparatus of claim 9, wherein the controllerfurther controls an operation of the transmission unit so as to vary acyclic prefix (CP) length of the OFDM symbol in the second slot intervalat each retransmission.
 11. The apparatus of claim 10, wherein thecontroller decreases the CP length in proportion to an increase in thenumber of the retransmissions.
 12. The apparatus of claim 9, wherein thecontroller further controls an operation of the transmission unit so asto vary a modulation order of the OFDM symbol in the second slotinterval at each retransmission.
 13. The apparatus of claim 12, whereinthe controller decreases the modulation order in proportion to anincrease in the number of the retransmissions.
 14. The apparatus ofclaim 9, wherein the controller is further configured to generate abroadcast overhead message including transmission format informationapplied to each of the first and second slot intervals using thetransmission unit, and broadcasts the generated broadcast overheadmessage using the RF unit.
 15. The apparatus of claim 9, wherein thecontroller is further configured to transmit a transmission formatapplied to each of the first and second slot intervals by performingscheduling with at least one of mobile stations receiving the broadcastphysical layer packet.
 16. The apparatus of claim 9, wherein the mobilecommunication system is a High Rate Packet Data (HRPD) system thattransmits the broadcast physical layer packet according to an OFDMtransmission scheme.